For cosmetic purposes, contact lenses having one or more colorants dispersed in the lens or printed on the lens are in high demand. These colored contact lenses enhance the natural beauty of the eye, or provide unique patterns on the iris of the wearer, or provide non cosmetic patterns or marks, such as rotation marks, inversion marks, product/brand codes, lot numbers, “DEMO” lenses, and the like, which are of benefits to wearers, eye-care practitioners and manufacturers.
Presently, methods of printing inks onto contact lens molds involve cliche ink transfer printing. A typical example of this printing follows. An image is etched into metal to form a cliché. The cliché is placed in a printer. Once in the printer, the cliché is inked by either an open inkwell doctoring system or by a closed ink cup sliding across the image. Then, a silicone pad picks up the inked image from the cliché and transfers the image to the contact lens. The silicone pads are made of a material comprising silicone that can vary in elasticity. The properties of the silicone material permit the inks to stick to the pad temporarily and fully release from the pad when it contacts the contact lens mold.
A number of inks are known in the art for cliché ink transfer printing of color images on a contact lens. Examples of such inks include those disclosed in U.S. Pat. Nos. 4,668,240, 4,857,072, 5,272,010, and 5,414,477. However, such inks known in the art are either incompatible with or incapable of producing a high quality color image on a nelfilcon (acrylate-modified PVA) contact lens when using a pad-printing system.
U.S. Pat. No. 6,162,844 to Lally, et al. discloses a introducing at least one polymeric dye and polyvinyl alcohol into a mold, and crosslinking or polymerizing to form a lens. Likewise, U.S. Pat. No. 6,149,842 to Lally, et al. teaches the making of a tinted lens by mixing a metal phthalocyanine dye or pigment with polyvinyl alcohol, which is then dispensed into a lens mold and crosslinked or polymerized to entrap the dye or pigment within the polymeric network of the lens. However, both result in a lens with dye or pigment dispersed throughout the lens, not an image printed on the surface or within the lens.
Copending U.S. Application Ser. No. 60/348,257, filed Nov. 7, 2001, by the present inventors discloses a colored ink to be printed upon a medical device by ink-jetting methods. However, consistent with the teachings of that application, every ink disclosed therein has a viscosity significantly lower than 50 centipoise. Such inks are inherently unsuitable for pad-printing methods.
Therefore, there exists a need for methods and inks suitable for producing a high-quality color image on a nelfilcon contact lens using a pad-printing system. There is also a need for methods for making such inks.